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I'm new to Analogue and I'm trying to find the Ideal filter for the following specifications:

  • $0.1\ \rm dB$ ripple
  • Cutoff Frequency $F_c = 80\ \rm{kHz}$
  • An attenuation of $40\ \rm dB$ at the stop-band frequency $F_s = 130 \ \rm kHz$

I'm not sure if I'm on the right path but till now with all the research I've done I think I have to use a Low pass, 7th order Chebyshev Filter (Type 1) using Sallen key topology (not sure why but I was thinking since it have less noise at a gain of 1 I should go with a Sallen-key).

Any help and explanation would be great!

Thanks in advance :)! Pix

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  • $\begingroup$ That looks very homework-ish. Why did you not choose an elliptic filter? Does the attenuation need to be 40dB at 130kHz, or does it need to be equal to or greater than 40dB at and above 130kHz? $\endgroup$
    – TimWescott
    Jan 11 '21 at 17:09
  • $\begingroup$ Yes it's actually a task I'm trying to figure out. the reason I didn't choose an elliptic filter is because the frequency between the cuttoff and the stopband is not as steep so i thought an elliptic is not ideal. Also when inputted the values into an automatic filter design it had two options, the butterworth and the chebyshev. (I choose chebychev for less components/orders). regarding Attenuation it have to be of 40dB at fs = 130kHz. $\endgroup$
    – Pix
    Jan 11 '21 at 19:17
  • $\begingroup$ I'm a bit unclear of what your question is -- it's more a statement, and a comment that "any help would be great". If it's that you just got those recommendations from a piece of software and you want to know why it may have made them, then edit your question to say so, and include the software you're using. $\endgroup$
    – TimWescott
    Jan 11 '21 at 20:24
  • $\begingroup$ Basically the question says: Design a filter with the following specs; Up to 0.1dB ripple, frequency cutoff of 80kHz and an attenuation of 40dB at fs = 130k. $\endgroup$
    – Pix
    Jan 11 '21 at 20:32
  • $\begingroup$ So, Stackexchange wants a discrete question with a provably correct answer. "Any help or comments would be great!" is an invitation for opinions and views, but is not a discrete question that can be given a provably correct answer. $\endgroup$
    – TimWescott
    Jan 11 '21 at 20:51

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